This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-185856, filed Jun. 30, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a method for correcting a mask pattern deviated due to the optical proximity effects that arise when a pattern of an exposure mask is transferred onto a substrate, and particularly relates to a method for correcting a mask pattern in consideration of various deviations that are assumed in the optical lithography process (deviations in exposure dose, focusing, etc.).
Further, the present invention relates to an exposure mask formed by using the above-mentioned correction method, and also relates to a storage medium which stores a program for executing the above-mentioned correction method by a computer.
Recently, along with micronization of the LSI, there has been elicited the optical proximity effects (OPE; hereinafter referred to as xe2x80x9cOPExe2x80x9d) wherein CD (critical dimension) deviation and geometric deformation occur between a pattern of an exposure mask and a pattern obtained on a wafer. Therefore, in order to obtain a desired pattern on the wafer, an optical proximity correction (OPC) technique for correcting a mask pattern in consideration with the influence of the OPE becomes necessary.
The conventional OPC technique is such that the OPE under a certain exposure condition (the exposure dose, the focal position) is predicted experimentally or by calculation and a mask pattern is corrected based on the prediction. However, along with the micronization of LSI patterns, permissible CD deviation when forming a transferred pattern becomes much smaller. Consequently, an OPC technique considering various deviations that arise when transferring a mask pattern (i.e. deviations in the focal position, the exposure dose, etc.) is desired.
For the OPC technique that considers the above-mentioned deviations, a method considering mainly the deviation in the focusing has been disclosed, for example, as described in a paper by John P. Stirniman et. al, xe2x80x9cFast proximity correction with zone sampling,xe2x80x9d Proceeding of SPIE, Vol.2197, pp.294-300. However, an optimum corrected pattern is not necessarily obtained by this technique when assuming the deviation in the exposure dose.
Also, regarding a memory cell section, there has been disclosed a correction method for maximizing both exposure dose range (i.e. exposure dose latitude) and focal range (i.e. the depth of focus) which can form the pattern within a predetermined amount of deviation in sizes, in a document by the present inventors (S. Inoue et. al), xe2x80x9cAutomatic optical proximity correction with optimization of stepper conditionxe2x80x9d, Proceeding of SPIE, Vol.2440, pp.240-251. However, this document treats only the correction in an extremely limited region, that is, within a single cell, and the correction calculation is performed using a kind of the random search method based on simulated annealing; therefore, when this method is applied to a random pattern, it takes too much time for the calculation and it is thought that the processing in a practical period of time is impossible.
As can be understood in the foregoing, when one wishes to correct the OPE on a mask pattern considering the margin of the exposure dose, a considerably increased time is conventionally required for the correction process, and hence high-speed processing is impossible, and that it is difficult to achieve correction accuracy sufficiently.
It is an object of the present invention to provide a method for correcting a mask pattern capable of performing high-precision correction in consideration of the margin of the exposure dose without greatly increasing the load of the OPC processing for a mask pattern.
Moreover, it is a further object of the present invention to provide an exposure mask that is formed using the above-mentioned correction method and capable of contributing the improvement of the accuracy of the pattern transferring.
Furthermore, it is another object of the present invention to provide a storage medium storing a program for making a computer execute the above-mentioned correction method.
A first aspect of the present invention is a method for correcting a mask pattern where a design mask pattern is corrected considering the influence of the OPE that arises when the design mask pattern is transferred onto a substrate, and provides a method for correcting a mask pattern comprising the steps of: correcting the mask pattern so that the edges of a transferred pattern formed at a predetermined focal position with a previously-given exposure dose are located at the desired edge location of the pattern within an amount of the displacement from a desired edge location of the pattern that is determined to be smaller than a previously-set permissible displacement of the edge; and adding additional correction to the mask pattern in order to achieve a desired depth of focus at a boundary of the exposure dose latitude.
According to the first aspect of the invention, in the additional correction, if the exposure dose required for obtaining a position of the edge of a desired transferred pattern is changed by xcex94E when the edges of an interest to-be-corrected pattern is moved a by xcex94L, the coefficient M, i.e., Exposure Dose MEF (Mask Enhanced Factor) is used, where it is determined by the following equation:
M=xcex94E/xcex94L.
A value obtained by dividing by the coefficient M a difference between an exposure dose for forming a desired edge displacement and the exposure dose latitude is added as a correction value to a pattern not satisfying a permissible edge position depending upon a boundary of the exposure dose latitude in a defocus position for obtaining a desired focal depth.
A second aspect of the present invention provides a method for correcting a mask pattern wherein a design mask pattern is corrected to suppress the influence of the OPE that arises when the design mask pattern is transferred onto a substrate, and specifically provides a method for correcting a mask pattern, the method comprising the steps of: extracting patterns in an OPE acting range; classifying the extracted patterns into to-be-corrected patterns whose edges are actually to be displaced and a reference pattern whose edges are not displaced in calculating the correction; and correcting the shape of the to-be-corrected patterns so that the to-be-corrected patterns all are transferred and finished onto a substrate with each edge being located within a permissible displacement of an edge.
The correction method according to the second aspect includes the step of adding an additional correction to the mask pattern to achieve a desired depth of focus with an exposure dose at a boundary of the exposure dose latitude.
According to the present invention, the edge position of a transferred pattern obtained at a predetermined focal position by a given exposure dose is corrected such that the edge position is within a displacement from a desired pattern edge position determined by a displacement amount xcex94pos1 smaller than a preset permissible edge displacement amount xcex94pos. Then, in order to consider the exposure dose, an additional correction is subjected to a mask pattern so that a desired focal depth is obtained at respective boundaries. As a result, a time required for a correction calculation is reduced in a large extent. A high precision correction can be performed without increasing the load for correction processing.
Further, the extracted patterns are classified into the to-be-corrected patterns and the reference patterns and only the to-be-corrected patterns are corrected, whereby interest pattern edges can be corrected in a high-accuracy manner while suppressing the load of the correction processing.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.